A process transmitter generally includes a transducer or sensor that responds to a process variable. A process variable generally refers to a chemical or physical state of matter or conversion of energy. Examples of process variables include pressure, temperature, flow, conductivity, pH, and other properties. Pressure is considered to be a basic process variable in that it can be used to measure flow, level, and even temperature.
Pressure transmitters are commonly used in industrial processes to measure and monitor pressures of various industrial process fluids, such as slurries, liquids, vapors, and gases of chemical, pulp, petroleum, gas, pharmaceuticals, food, and other fluid-type processing plants. Differential pressure transmitters generally include a pair of process pressure fluid inputs which are operably coupled to a differential pressure sensor (within the transmitter) that responds to the difference in pressure between the two inputs. Differential pressure transmitters typically include a differential pressure sensor operably coupled to a pair of isolator diaphragms. The isolator diaphragms are positioned at the process fluid inlets and isolate the differential pressure sensor from the harsh process fluids being sensed. Pressure is transferred from the process fluid to the differential pressure sensor through a substantially incompressible fill fluid carried in a passageway extending from the isolator diaphragm to the differential pressure sensor.
Process fluid pressure transmitters are generally coupled to the process via an instrument manifold or flange. One type of arrangement provides an instrument manifold that presents the process fluid pressure inlets in a pair of substantially coplanar ports. One example of such a manifold is sold under the trade designation Model 305 Coplanar™ available from Rosemount Inc., of Chanhassen, Minn. The coplanar design enables flangeless valve integration, and generally provides a compact, light-weight assembly. Moreover, the coplanar design facilitates in-process calibration, and provides substantially fewer possible leak points than conventional non-planar manifold-transmitter assemblies.
A process fluid pressure transmitter is generally considered a field device and that it is able to be mounted in the field. “Field” is generally an external area in a process installation that may be subject to climatological extremes, vibration, changes in humidity, electromagnetic or radiofrequency interface, or other environmental challenges. Thus, the robust physical package of a process fluid pressure transmitter provides the transmitter with the ability to operate in the “field” for extended periods (such as years) at a time.